U.S. patent application number 10/132203 was filed with the patent office on 2003-02-27 for method for the generation of modulation by frequency division followed by frequency multiplication, and radiofrequency apparatus.
This patent application is currently assigned to THALES. Invention is credited to Boutigny, Pierre-Henri, Collin, Laurent, Triquenaux, Denis.
Application Number | 20030040289 10/132203 |
Document ID | / |
Family ID | 8862796 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030040289 |
Kind Code |
A1 |
Collin, Laurent ; et
al. |
February 27, 2003 |
Method for the generation of modulation by frequency division
followed by frequency multiplication, and radiofrequency
apparatus
Abstract
Method and radiofrequency apparatus comprising at least one
transmitter and/or one receiver of one or more useful signals
comprising at least one device adapted to applying a coefficient
(N, K.sub.1, K.sub.2) to the useful signal or signals. Application
to BPSK or QPSK type modulation.
Inventors: |
Collin, Laurent; (Paris,
FR) ; Boutigny, Pierre-Henri; (Melun, FR) ;
Triquenaux, Denis; (Versailles, FR) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
THALES
PARIS
FR
75008
|
Family ID: |
8862796 |
Appl. No.: |
10/132203 |
Filed: |
April 26, 2002 |
Current U.S.
Class: |
455/91 |
Current CPC
Class: |
H04L 27/2007 20130101;
H03D 7/161 20130101; H04L 27/20 20130101; H04L 27/2078
20130101 |
Class at
Publication: |
455/91 |
International
Class: |
H04B 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 2001 |
FR |
01 05730 |
Claims
What is claimed is:
1. A radiofrequency apparatus comprising at least one transmitter
and/or one receiver of one or more useful signals, wherein the
apparatus comprises at least one modulator adapted to the
modulation of the useful signal or signals at a frequency F.sub.m,
F.sub.mv, a device adapted to the division of the modulated signal
or signals by a coefficient K.sub.1, K.sub.2, a device to transpose
the modulated and divided signal or signals into a frequency
F.sub.r, a device to multiply the modulated, divided and transposed
signal or signals by a coefficient N in order to obtain a signal at
a transmission frequency F.sub.e.
2. An apparatus according to claim 1, wherein the modulator
comprises an integrated divider.
3. An apparatus according to claim 1, wherein the divider is
positioned after the modulator.
4. An apparatus according to one of the claims 1 to 3, comprising a
device for the random generation of a formant.
5. An apparatus according to claim 4, wherein the device for the
generation of a formant is adapted to producing a formant enabling
the optimizing of the phase states during the modulation of the
useful signal and/or ensuring a random sense of phase rotation.
6. An apparatus according to one of the claims 1 to 5, forming a
transmitter and wherein it comprises a device for transposing the
frequency of the modulated and divided signals, this device being
located between the divider and the multiplier.
7. A method for the transmission of one or more useful signals
comprising at least the following steps: Modulating the useful
signal or signals at a frequency F.sub.m, F.sub.mv, Dividing the
modulated useful signal or signals by a coefficient K.sub.1,
K.sub.2, Transposing the modulated and divided signal or signals
S'.sub.3 into a frequency F.sub.r, Multiplying the modulated,
divided and transposed signal or signals by a coefficient N in
order to obtain a signal at this transmission frequency
F.sub.e.
8. A method according to claim 7, comprising a step for the
preceding of the useful signal or signals wherein the sense of the
phase rotation to meet the different points of the constellation of
the phase states of the modulation is determined randomly.
9. A method according to claim 8, wherein the paths and the sense
of the phase rotation to go to the different points of the
constellation chosen are for example randomly distributed between
the different states in order to obtain the most symmetrical
possible spectrum after frequency division and frequency
multiplication.
10. A method according to one of the claims 8 to 9, wherein the
path is determined to modify the power spectral density, especially
in order to reduce the level of the minor lobes of the spectral
density of the useful signal.
11. A method according to the claims 8 to 10, wherein the sense of
phase rotation is determined by random draw after the path to be
taken has been determined.
12. A method according to one of the claims 7 to 11, wherein the
modulation of the useful signal is carried out for example by a
vector modulator enabling modulation at constant amplitude.
13. An application of the method according to claims 7 to 12, to a
BPSK or QPSK type modulation.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a radiocommunications
apparatus comprising means suited to the application of a
coefficient to one or more useful signals.
[0003] The expression "useful signal" hereinafter designates an
information-carrier signal.
[0004] The coefficient may be a multiplication coefficient or,
again, a division coefficient.
[0005] The radiocommunications apparatus comprises, for example, a
transmitter and/or a receiver, at least one of these two devices
comprising the division and/or multiplication means.
[0006] It can be applied to phase modulation and/or frequency
modulation.
[0007] It relates especially to radiocommunications apparatuses
(using wireless beams, unicast links, and unicast-multicast links
etc) working in the millimeter frequency band.
[0008] 2. Description of the Prior Art
[0009] In radiocommunications apparatuses, the transmission system
generally comprises a device to transpose the frequency of the
information-carrying useful signal into a radiofrequency band. The
frequency F.sub.ol of the local oscillator is therefore of the same
magnitude as the transmission frequency F.sub.e. This entails the
development of functions in frequency ranges, especially in the
millimeter range, that are difficult to attain.
[0010] There are also known transmission systems where the
frequency multiplication step is performed on the signal that has
undergone frequency transposition.
[0011] The idea of the invention is based on the structure of a
transmitter and/or receiver that integrates devices adapted to the
application of a coefficient to one or more useful signals.
[0012] Furthermore, the structure comprises means adapted to
improving the symmetry of the power spectral density obtained by
this method. It optimizes the baseband modulating signals to filter
the power spectral density of the initial modulating signal at
transmission.
SUMMARY OF THE INVENTION
[0013] The object of the invention relates to a radiofrequency
apparatus comprising at least one transmitter and/or one receiver
of one or more useful signals, wherein the apparatus comprises at
least one modulator adapted to the modulation of the useful signal
or signals at a frequency F.sub.m, F.sub.mv, a device adapted to
the division of the modulated signal or signals by a coefficient
K.sub.1, K.sub.2, a device to transpose the modulated and divided
signal or signals into a frequency F.sub.r, a device to multiply
the modulated, divided and transposed signal or signals by a
coefficient N in order to obtain a signal at a transmission
frequency F.sub.e.
[0014] It comprises for example a divider integrated into the
modulator.
[0015] According to another embodiment, the equipment comprises at
least one divider device positioned after the modulator.
[0016] According to another embodiment, the equipment comprises at
least one divider device positioned after the modulator.
[0017] It may comprise a device for the random generation of a
formant, which can be adapted to produce a formant enabling the
optimizing of the phase states during the modulation of the useful
signal and/or ensuring a random sense of phase rotation.
[0018] The radiofrequency apparatus is for example a transmitter
comprising at least one of the above-mentioned characteristics and
a device for transposing the frequency of the modulated and divided
signals, located between the divider and the multiplier.
[0019] The invention also relates to a method for the transmission
of one or more useful signals comprising at least the following
steps:
[0020] Modulating the useful signal or signals at a frequency
F.sub.m, F.sub.mv,
[0021] Dividing the modulated useful signal or signals by a
coefficient K.sub.1, K.sub.2,
[0022] Transposing the modulated and divided signal or signals
S'.sub.3 into a frequency F.sub.r,
[0023] Multiplying the modulated, divided and transposed signal or
signals by a coefficient N in order to obtain a signal at this
transmission frequency F.sub.e.
[0024] It may comprise at least one step for the precoding of the
useful signal or signals wherein the sense of the phase rotation to
meet the different points of the constellation of the phase states
of the modulation is determined randomly.
[0025] The paths and the senses of phase rotation to go to the
different points of the constellation chosen are for example
randomly distributed between the different states in order to
obtain the most symmetrical possible spectrum after frequency
division and frequency multiplication.
[0026] The path is determined for example to modify the power
spectral density, especially in order to reduce the level of the
minor lobes of the spectral density of the useful signal.
[0027] The sense of phase rotation is determined by random draw
after the path to be taken has been determined.
[0028] The modulation of the useful signal is carried out for
example by a vector modulator enabling modulation at constant
amplitude.
[0029] The method can be applied for example to a BPSK or QPSK type
modulation.
[0030] The invention offers especially the following
advantages:
[0031] The simplification of the architecture of the high frequency
part of a transmission system.
[0032] The use of a minimum quantity of components in the
radiofrequency part of the transmitter, for example.
[0033] Precision in the initial modulation which is of the same
magnitude as the precision required in the modulation after
multiplication if the ratio of division on the initial modulation
is identical to the multiplication ratio.
[0034] The transposition of the modulation at output of the divider
enabling an increase in the frequency of the useful signal divided
before it is multiplied it and therefore the obtaining, at output
of the multiplier, of a transmission signal towards the microwave
or millimeter frequency ranges with a reasonable multiplication
ratio.
[0035] An optimization of the symmetry of the spectrum emitted and
a filtering of the power density of the useful signal by optimizing
the formant of the signals in phase and in quadrature of the
modulator carrying out the initial modulation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Other advantages and characteristics of the invention shall
appear more clearly from the following description, given by way of
an illustration that in no way restricts the scope of the
invention, with reference to the appended drawings, of which:
[0037] FIG. 1 is a drawing of the transmission system comprising a
prior art multiplication device,
[0038] FIG. 2 shows a first structure of the transmission system
according to the invention, including a useful signal divider,
[0039] FIG. 3 shows a second structure of a transmission
system,,
[0040] FIG. 4 shows an alternative embodiment combining the
structures of FIGS. 2 and 3,
[0041] FIGS. 5 to 12 show exemplary signals and spectra obtained
with the structure according to the invention.
MORE DETAILED DESCRIPTION
[0042] In order to provide for a clearer understanding of the
object of the invention, the following description, given by way of
an illustration that in no way restricts the scope of the
invention, pertains to a transmission system of a radiofrequency
apparatus incorporating a device adapted to performing a frequency
division of the useful signal and a device adapted to performing a
frequency multiplication of the useful signal that has undergone
frequency division and transposition.
[0043] FIG. 1 shows an exemplary transmission system of a
radiofrequency apparatus including a device for the frequency
multiplication of the useful signal.
[0044] The system comprises a modulator 1 giving a useful,
information-carrier signal S.sub.1 that is phase modulated and has
a frequency F.sub.m, a local oscillator 2 at a frequency F.sub.ol
and a mixer 3. This mixer 3 receives the modulated useful signal
and a signal S.sub.2 at the frequency F.sub.ol in order to mix them
and produce a signal S.sub.3 at a frequency F.sub.r that is equal
or substantially equal to (F.sub.m+F.sub.ol) or
(F.sub.m-F.sub.ol).This frequency-transposed signal S.sub.3 is sent
to a bandpass filter 4 and then to a device 5 adapted to the
multiplication of this signal S.sub.3 by a coefficient N so as to
produce a signal S.sub.4 at the transmission frequency F.sub.e(with
F.sub.e=N(F.sub.ol+F.sub.m) or F.sub.e=N(F.sub.ol-F.sub.m)). The
multiplied signal is then sent to a second bandpass filter 6 and
then to an amplifier 7 by which it is given the power sufficient
for it to be transmitted at the antenna output 8 as the signal
S.sub.5.
[0045] Should the useful signal at the output of the antenna be a
signal at the frequency F.sub.e modulated by phase jumps
i*(2*.pi./m) corresponding to the encoding of the digital data to
be transmitted, where m is the number of states of the phase
modulation, the phase jumps at the antenna are equal to: 1 i
.times. 2 m with i [ 0 , , m - 1 ] , or ( 2 i + 1 ) .times. m with
i [ 0 , , ( m / 2 ) - 1 ] ( 1 )
[0046] The coefficient m is a function of the modulation to be
sent. If m=2.sup.r, where r is a coefficient depending on the phase
modulation used, we have, for example BPSK (Bit Phase Shift Keying)
modulation for r=1 and m=2 and QPSK (Quadrature Phase Shift Keying)
for r=2 and m=4.
[0047] This phase modulation is the phase modulation achieved at
output of the multiplier by N, N being the multiplication factor.
The multiplication by N of a signal with a frequency F.sub.r and an
initial phase .phi..sub.0r creates a transmission frequency
F.sub.e=N*F.sub.r and a phase rotation of N*.phi..sub.0r.
[0048] It is therefore possible to obtain the signal at the
frequency F.sub.e modulated by phase jumps i*(2*.pi./m), if the
signal at the frequency F.sub.r is modulated by phase jumps
i*(2*.pi./m)/N.
[0049] In this case, the phase jumps at the reference signal
F.sub.r are equal to: 2 i .times. 2 / m N with i [ 0 , , m - 1 ] ,
or ( 2 i + 1 ) .times. / m N with i [ 0 , , ( m / 2 ) - 1 ] , ( 2
)
[0050] Should the signal with the frequency F.sub.r results from a
transposition of the signal at the frequency F.sub.m,
phase-modulated with a local oscillator F.sub.ol, the phase
modulation of the signal F.sub.m is identical to the phase
modulation of the signal F.sub.r. Following transposition, the
frequency F.sub.r is equal to (F.sub.ol+F.sub.m) or
(F.sub.ol-F.sub.m) depending on the filtering used at output of the
mixer making the transposition.
[0051] The phase jumps for the signal F.sub.m are therefore
identical to the phase jumps for F.sub.r which are necessary to
obtain the phase modulation i*(2*.pi./m) desired at the antenna.
These phase jumps therefore, at the level of the modulated signal
F.sub.m, are equal to: 3 i .times. 2 / m N with i [ 0 , , m - 1 ] ,
or ( 2 i + 1 ) .times. / m N with i [ 0 , , ( m / 2 ) - 1 ] , ( 3
)
[0052] This modulation which makes it possible to obtain the phase
modulation i*(2*.pi./m) after multiplication by N is not the only
one possible. In particular, if N is an odd number and greater than
m-1, phase jumps of i*(2*.pi./m) become phase jumps N*i*(2*.pi./m)
following multiplication by N: all the states modulo 2.pi. are
obtained following multiplication by N.
[0053] A phase modulation may be generated, for example, by a
vector modulator which is used to sum two modulations that come
from a same oscillator but are phase-shifted by .pi./2, from two
modulating signals m.sub.l (t) and m.sub.Q (t) related to the
message to be transmitted.
[0054] There are several devices used to obtain a modulation with
phase jumps of the type 4 i .times. 2 / m N or ( 2 i + 1 ) .times.
/ m N .
[0055] Hereinafter in the description, identical references
designate similar elements.
[0056] FIG. 2 gives a schematic view of the structure of a
transmitter according to the invention, comprising means used to
divide the useful signal before multiplying it in a system as
described in FIG. 1.
[0057] The transmitter comprises different elements which may be
grouped into two blocks I and II. The first block I has the
function especially of modulating and dividing the signal to be
transmitted while the block II has the function of multiplying and
amplifying the divided and transposed signal S'.sub.3 before it is
transmitted. The two blocks may form part of one and the same
device or be distinct.
[0058] The binary message S.sub.0 to be transmitted is first of all
subdivided into two elementary modulating signals m.sub.Q and
m.sub.l by applying a formant (t) function 9. A formant function
(t) corresponds to an elementary relationship by which it is
possible to pass from one state to another. This function is
defined on the duration of a bit of the signal S.sub.0 and its
amplitude is standardized at 1. This can be applied, of course, to
digital or analog messages.
[0059] The elementary modulating signals are then transmitted to a
vector modulator 10 integrating a phase divider with a coefficient
K.sub.1.
[0060] The modulating signals m.sub.l and m.sub.Q linked to the
message to be transmitted are such that (5): 5 m e + jm Q = 1
.times. exp ( j ( 2 i + 1 ) .times. / m K 1 )
[0061] with K.sub.1=N or K.sub.1
[0062] substantially equal to N with N being the factor of
multiplication that is an even or odd whole number.
[0063] FIG. 3 gives a schematic view of a second alternative
embodiment of a device enabling this same modulation. In this case,
the vector modulator 11 is associated with a frequency divider 12
placed between this modulator and the transposition mixer 3. This
frequency divider 12 divides the useful signal having a frequency
F.sub.mv at output of the vector modulator 11 by a coefficient
K.sub.2 equal or substantially equal to N, and then carries out the
operation of mixing with the frequency F.sub.0l coming from the
local oscillator and then the multiplication by N. The modulating
signals m.sub.l and m.sub.Q related to the message to be
transmitted are determined from the expression (5) with
K.sub.1-1.
[0064] The division by K.sub.2 of a signal with a frequency
F.sub.mv and an initial phase .phi..sub.mv creates a modulation
frequency F.sub.m=F.sub.mv/K.sub.2 and a phase rotation of
.phi..sub.mv/K.sub.2
[0065] For certain modulations, the use of a frequency divider not
integrated into the modulator is the cause of dissymmetry in the
frequency spectrum. This dissymmetry is expressed especially by a
shift in the frequency from its origin value and/or a dissymmetry
in the minor lobes of the spectrum.
[0066] To compensate for these defects, the transmission system may
comprise a device adapted to the generation of a random sense of
phase rotation to go from one state to another and/or adapted to
determining the formants used to optimize the transitions between
the logic states and prevent dissymmetry in the minor lobes.
[0067] The result thereof is an optimization of the transitions
between the logic states and the passages between the different
states throughout the constellation of the states of the modulation
used and a sense of rotation that is not always identical. The use
of a random sense of rotation can be used especially to re-center
the frequency.
[0068] The sense of phase rotation to meet the different points of
the constellation of the phase states is determined for example
randomly by a data preceding method.
[0069] The formant function used to go from one state to another is
such that the paths and the senses of phase rotation taken to go to
the different points of the constellation chosen are distributed
randomly between the different states in order to obtain the most
symmetrical spectrum possible after a frequency division and
frequency multiplication.
[0070] The path is determined to modify the power spectral density
in order especially to reduce the level of the minor lobes of the
spectral density of the transmitted signal.
[0071] The sense of phase rotation is determined by random draw
after the path to be traveled has been determined.
[0072] This can be applied especially to BPSK or QPSK modulations
or again for any other modulation generating dissymmetry in the
spectrum of the frequencies.
[0073] FIG. 4 gives a schematic view of a third alternative
embodiment of a transmitter structure enabling this same modulation
by a mixing of the two alternative embodiments described in FIGS. 2
and 3. In this case, the phase division is distributed between the
phase divider K.sub.1 integrated into the vector modulator 10 and a
frequency divider K.sub.2 placed between the vector modulator 10
and the transposition mixer 3: the division factors K.sub.1 and
K.sub.2 are chosen so that K.sub.1*K.sub.2=N, the multiplication
factor of the frequency multiplier. In this case, we truly obtain a
phase modulation equal to .phi..sub.m/N.
[0074] In practice, in all the exemplary embodiments mentioned here
above, the frequency divider may be made by logic circuits based on
flip-flop circuits used for the storage and therefore for the
counting of the passages through zero of the signal at its input.
The divider divides the phase information but generally loses the
information on amplitude modulation because it processes only
transitions. To overcome this drawback, which leads to a
transformation of the initial modulation before division, it is
possible to use a vector modulator adapted to the generation of a
constant amplitude modulation.
[0075] The method implemented in a transmitter may comprise the
following steps:
[0076] 1) applying a formant to the binary message to be
transmitted in order to obtain to elementary modulating signals
m.sub.Q and m.sub.l,
[0077] 2) dividing the modulator signal by a coefficient K equal or
substantially equal to the multiplication coefficient N used
further below in the transmission system,
[0078] 3) transposing the frequency signal by means of the
frequency F.sub.ol of the oscillator,
[0079] 4) multiplying the frequency-transposed signal by the
multiplier coefficient N,
[0080] 5) transmitting the signal after amplification to the
required transmission level
[0081] The modulation and division steps can be carried out of the
same time.
Exemplary Application in the Framework of a BPSK Type
Modulation
[0082] In the case of a two-phase-state BPSK type modulation, the
division of the modulating signal by a factor K.sub.2=2, introduces
a constellation with four phase states at output of the divider.
The BPSK modulation has a two-phase-state constellation: the
division by K.sub.2=2 introduces a phase ambiguity equal to
.pi.(2.pi./K.sub.2). This ambiguity is lifted after the
multiplication by 2. In practice, this division leads to a
dissymmetry in the power spectral density of the useful signal that
is inherent in the distribution of the transitions between the
states of the initial constellation.
[0083] Should the BPSK modulation divided by K.sub.2 be done
directly by the vector modulator, the modulation may generate a
constellation with 2 phase states, for example exp(+j
(.pi./2)/K.sub.2) and exp(-j (.pi./2)/K.sub.2). This modulation has
a power spectral density of the sin(x)/x type symmetrical with
respect to the carrier with a line at the frequency of the
carrier.
[0084] Should the BPSK modulation be done by the vector modulator
and the frequency division by a digital divider K.sub.2, the
modulator manages a constellation with two phase states for example
exp(+j (.pi./4)) and exp(-j (3.pi./4)). The division by K.sub.2=2
has the effect of creating a constellation with four phase states
corresponding for example to the point exp(+j (.pi./4), exp(-j
(.pi./4), exp(+j (3.pi./4)) and exp(-j (3.pi./4)). The phase
modulation with phase jumps of +/-i*.pi./2, thus made, has a
dissymmetry related to the non-random character of the inter-state
transitions: a dissymmetry of the power spectral density with
respect to its center frequency and a shifting of the center
frequency of the spectrum.
[0085] The dissymmetry of the power spectral density is related to
the physical impossibility of obtaining a perfect BPSK phase
modulation. To go from one point of the constellation to another,
the BPSK modulator will impose a sense of phase rotation
corresponding to the passage from the point at +.pi./4 to the point
at -3.pi./4 and a phase rotation sense corresponding to the passage
from the point at -3.pi./4 to the point +.pi./4: in practice, the
constellation cannot be perfectly zero; the "zero" point cannot be
reached.
[0086] If we consider a BPSK modulation made from a perfect
modulator vector associated with one and the same message on both
modulation channels, namely the I and Q channels, the introduction
of a different filtering operation between the I and Q channels
will give rise to a sense of rotation to go from one point of the
constellation to another. This rotational sense is identical
between the two states, but the fact of transposing the filters
causes a change in the sense of rotation to go from one point to
another in the constellation.
[0087] By way of an example, FIGS. 5 and 6 respectively give the
shapes of the spectra of the BPSK modulating signal before and
after division by 2 as a function of the filtering operations
carried out on the I and Q signals of the vector modulator.
[0088] These curves are plotted in a spectral density graph
expressed in dBc as a function of the frequency F.sub.m related to
its carrier in MHz. They are obtained under the following
conditions:
[0089] FIG. 5:
General Simulation Parameters
[0090] rough BPSK modulation (I=Q without formant)
[0091] random binary message 10 Mbits per second on carrier at 200
MHz
[0092] center frequency 200 MHz and sampling frequency 4 GHz
Parameters of the Curves
[0093] curve 1: baseband filtering 50 MHz I channel and 100 MHz Q
channel
[0094] curve 2: baseband filtering 100 MHz I channel and 50 MHz Q
channel
[0095] FIG. 6:
General Simulation Parameters
[0096] rough BPSK modulation (I=Q) after frequency divider K2=2
[0097] random binary message 10 Mbits per second on carrier at 200
MHz
[0098] center frequency 100 MHz and sampling frequency 4 GHz
Parameters of the Curves
[0099] curve 1: baseband filtering 50 MHz I channel and 100 MHz Q
channel
[0100] curve 2: baseband filtering 100 MHz I channel and 50 MHz
channel
[0101] The power spectral density after division has
discontinuities at frequencies which are multiples of the bit rate.
These discontinuities change direction according to the sense of
rotation of the constellation.
[0102] The fact of keeping the same rotational sense to go from one
state to another leads to a shift in the frequency of the spectrum.
This shift in frequency depends on the nature of the message and,
more particularly, on the mean number of transitions between
states. The maximum frequency shift corresponds to a message in
which the two logic states are alternated: in this case, the phase
of the modulating signal rotates by .pi. radians per bit with
respect to the carrier and, therefore, the shift in frequency is
equal to:
.DELTA.F=(1/2.pi.)*(.DELTA..PHI./.DELTA.t)/N=(Fbit rate/2)/N.
[0103] FIG. 7 shows the shape of the spectrum of the initial BPSK
modulation and of the spectrum after division by 2 and
multiplication by 2 for a value of filtering of the I and Q
modulation channels.
[0104] Conditions for obtaining the curves of FIG. 7:
General Simulation Parameters
[0105] rough BPSK modulation l=Q but baseband filtering 100 MHz I
channel and 50 MHz Q channel
[0106] random binary message 10 Mbits per second on carrier at 200
MHz
[0107] center frequency 200 MHz and sampling frequency 4 GHz
Parameters of the Curves
[0108] curve 1: initial BPSK modulation at output of the vector
modulator
[0109] curve 2: BPSK modulation after divider by 2 and multiplier
by 2
[0110] A dissymmetry is observed essentially between the minor
lobes but, on the whole, the spectrum is centered on the carrier
frequency.
[0111] To make the spectrum of the modulation more symmetrical at
output of the divider and therefore more symmetrical at output of
the multiplier, the transitions between the logic states must be
optimized and it must be ensured that the passages between the
different states are all made on the constellation and that the
phase rotation sense is not always identical.
[0112] In the case of a BPSK modulation, the fact of choosing a
different sense of rotation for the passage between the two states
symmetrizes the divided spectrum (identical path to go from one
point to another but with a different rotational sense). However,
lines appear at the frequencies that are multiples of the bit rate
(with respect to the carrier). To eliminate these lines that are
multiples of the bit rate, the direction of the passage from one
state to another must be randomly distributed.
[0113] Improving the symmetry of the power spectral density of a
modulation made by a frequency division followed by a frequency
multiplication therefore relies on an equiprobable distribution of
the two senses of phase rotation to go from one state to another:
the paths between the states are, of course, symmetrical.
[0114] For certain phase modulations, where there is for example a
precoding of the data before the modulator, these conditions may be
fulfilled. For other modulations such as the BPSK or QPSK
modulations, the sense of the phase rotation for a jump equal to
.pi. depends on the dissymmetries of the modulator, and it is
always identical.
[0115] Dictating a path, to go from one point of the constellation
to another, amounts to filtering the modulating signal and
therefore to filtering the spectral density of the initial
modulation. If this filtering does not affect the amplitude of the
modulated signal, the modulation coming from the vector modulator
is preserved throughout the transmission system, even if the system
comprises, as in the present case, a frequency divider, a frequency
multiplier or a saturated amplifier.
[0116] To obtain a modulated signal with a constant amplitude, it
is enough for the modulating signals m.sub.l(t) and m.sub.Q(t) to
verify the relationship
.vertline.m.sub.l(t)+jm.sub.Q(t).vertline.=1 at each instant. This
corresponds to a phase or frequency modulation .phi..sub.0m(t) such
that m.sub.l(t)+jm.sub.Q(t)=exp(+j.phi..sub.m(t)). From the
viewpoint of the constellation, the fact of generating a signal at
constant amplitude amounts to moving in a circle. The choice of the
filtering amounts to determining a relationship, as a function of
time, of the phase of the modulating signal.
[0117] In the case of the above-mentioned example of BPSK
modulation, exemplary phase relationships used to modify the
spectral congestion of the modulation and symmetrize the spectral
density once divided are given here below.
[0118] For these examples, the sense of the phase rotation between
two states is determined by comparing the current state with the
preceding state and by choosing the sense of the phase rotation
between the states by random draw.
[0119] For a BPSK modulation, table 1 gives the phase relationship
on the duration of a bit as a function of the state of this bit
X.sub.k and of the previous bit X.sub.k-1, the result of the random
draw TA.sub.k as well as the formant of the formant(t) modulating
signal. The formant(t) function corresponds to the elementary phase
relationships used to pass from one state to another. It is defined
according to the duration of one bit and its amplitude is
standardized at 1, it being known that, in the case of a BPSK
modulation, the phase variation on one bit is equal to .pi.
radians.
1TABLE 1 The different phase states of a BPSK modulation with
formant and random sense of phase rotation. Result of Phase
.PHI..sub.0m of Current Preceding random the modulating signal on
the Shape of the phase bit bit draw duration of the bit on the
duration of X.sub.k X.sub.k-1 TA.sub.k
t.epsilon.[t.sub.k,t.sub.k+1] the bit 0 0 0 or 1 .PHI..sub.k(t) =
.PHI..sub.k-1(t = Tbit) = 0 Constant phase 0 1 0 .PHI..sub.k(t) = +
.pi. * formant(t) Transition 0 at .pi. 0 1 1 .PHI..sub.k(t) = -
.pi. * formant(t) Transition 0 at .pi. 1 1 0 or 1 .PHI..sub.k(t) =
.PHI..sub.k-1(t = Tbit) = .pi. or -.pi. Constant phase 1 0 0
.PHI..sub.k(t) = + .pi. * [1-formant(t)] Transition .pi. at 0 1 0 1
.PHI..sub.k(t) = -.pi. * [1-formant(t)] Transition -.pi. at 0
[0120] FIG. 8 gives a view, by way of an illustration, of three
types of formant: a "rising time" type of formant F.sub.1, a cosine
type of formant F.sub.2 and a "linear phase" type of formant
F.sub.3. The temporal expressions of these formants are given in
the table 2.
2TABLE 2 Expressions of possible formants for the BPSK modulation
Type of formant Expression of the formant as a function of x =
t/Tbit 1st case: Formant(x) = 0 for x.epsilon.[0, (1 - x.sub.m)/2]
"rising time" type Formant(x) = (1/x.sub.m) * [x - (1 - x.sub.m)/2]
for x.epsilon.[(1- x.sub.m)/2, (1 + x.sub.m)/2] formant Formant(x)
= 1 for x.epsilon.[(1 + x.sub.m)/2,1] with x.sub.m = rising
time/Tbit 2nd case: Formant(x) = (1/2)*[1 - cos (.pi. x)] for
x.epsilon.[0, 1/2] "cosine" type Formant(x) = (1/2)*[1 + cos
(.pi.(1 - x))] for x.epsilon.[1/2, 1] formant 3rd case: Formant(x)
= x for x.epsilon.[0,1] "linear phase" type formant
[0121] FIG. 9 gives the shape of the spectra of the BPSK modulation
obtained by simulation for all three types of formants presented.
The choice of a formant on the phase modulation significantly
reduces the level of the distant minor lobes.
[0122] Conditions in which the curves of FIG. 9 are obtained:
General Simulation Parameters
[0123] BPSK modulation with formant
[0124] random binary message 10 Mbits per second on carrier at 200
MHz
[0125] center frequency 200 MHz and sampling frequency 4 GHz
Parameters of the Curves
[0126] curve 1: BPSK modulation with "rising time" type formant
(Tm=10%)
[0127] curve 2: BPSK modulation with "cosine" type formant
[0128] curve 3 : BPSK modulation with "linear phase" type
formant
[0129] FIG. 10 gives the shape of the spectra of the BPSK
modulation after division by 2 for all three types of formants
presented. The introduction of the random draw for the sense of the
phase rotation gives a better symmetry of the spectral density and
a center frequency after division equal to the carrier frequency
without modulation (at output of the divider).
[0130] Conditions in which the curves of FIG. 10 are obtained:
General Simulation Parameters
[0131] BPSK modulation with formant
[0132] random binary message 10 Mbits per second on carrier at 200
MHz
[0133] center frequency 200 MHz and sampling frequency 4 GHz
Parameters of the Curves
[0134] curve 1: BPSK modulation with "rising time" type formant
(Tm=10%)
[0135] curve 2 : BPSK modulation with "cosine" type formant
[0136] curve 3: BPSK modulation with "linear phase" type
formant
[0137] FIG. 11 gives the shape of the spectra of the BPSK
modulation after division by 2 and then multiplication by 2 for all
three types of formants presented.
[0138] Conditions in which the curves of FIG. 11 are obtained
General Simulation Parameters
[0139] BPSK modulation with formant
[0140] random binary message 10 Mbits per second on carrier at 200
MHz
[0141] center frequency 200 MHz and sampling frequency 4 GHz
Parameters of the Curves
[0142] curve 1: BPSK modulation with "rising time" type formant
(Tm=10%)
[0143] curve 2: BPSK modulation with "cosine" type formant
[0144] curve 3: BPSK modulation with "linear phase" type
formant
[0145] FIG. 12 gives the result of a spectral density obtained with
a BPSK modulation with "cosine" type formant and a random draw of
the sense of the phase rotation. In this embodiment, with a useful
bit rate of 1 Mbits/s, the useful signal is generated by a
modulator vector at 1890 MHz. It is divided by a frequency divider
by K.sub.2=16. Then, this signal is transposed by means of a local
oscillator at Frf=2375 MHz to obtain a BPSK modulated signal
filtered in the millimeter band after multiplication by N=16 and
therefore at Fe=38 GHz.
* * * * *